This invention relates to a liquid developing apparatus for electrophotography, in which a number of horizontally spaced developing electrodes are disposed very near the undersurface of a photoreceptor, which surface bears a latent electrostatic image, and said electrodes have an improved vertical cross-sectional shape to facilitate the movement of toner particles to the latent electrostatic image on the undersurface of the photoreceptor, whereby an electrophotographic image can be obtained having a high quality and free from non-uniformity of image density, edge effect and flow of image or streaks.
In electrophotography, the surface of a photoreceptor is charged, and then exposed to image light to form a latent electrostatic image thereon, after which the latent image is developed with toner particles. As the developing system, there are known cascade development, fur brush development, liquid development and the like, among which liquid development is suitable when aiming at preparing a high quality image having a high resolving power.
On the other hand, in such an electrophotographic development, in general, edge effect, streaks, halo effect and the like tend to occur, and in order to prevent these, for example, a method of disposing the developing electrodes in parallel to and near the photoreceptor is usually used. The effect of the developing electrodes is increased as the distance between the photoreceptor and the developing electrodes is narrowed. However, when the distance is too narrow it becomes difficult to supply a sufficient amount of a developer in which toner particles are suspended at the desired concentration in the gap between the photoreceptor and the developing electrodes, whereby the amount of the toner particles contacted with the photoreceptor is decreased and hence an image having the desired density cannot be obtained. Moreover, an image density gradient is formed in the direction of the relative flow of the liquid developer, and hence, the reproduction of a precise image becomes impossible. In order to solve this problem, for example, a proposal has been made for making a plurality of pores or slits in the developing electrodes to facilitate the supply of a sufficient amount of a liquid developer in which toner particles are suspended at the desired concentration through the pores or slits. However, such a proposal is not necessarily satisfactory, and in particular, when the moving speed of the photoreceptor is increased, no uniform image density is obtained and a flow of the image or streaks are caused.
Furthermore, when the photoreceptor is moved at a speed relative to the liquid developer, it has been found that a boundary layer is formed which starts at the forward end of the photoreceptor in relation to the direction of movement and the thickness of which layer increases as the layer approaches the backward end, and therefore, even if pores or slits are made in the developing electrodes the liquid developer cannot sufficiently pass through the gaps between the photoreceptor and the developing electrodes owing to resistance caused by viscous friction, and hence, an advantage of making the pores or slits in the developing electrodes is difficult to obtain. In addition, when the liquid developer is forcibly passed through the gap between the photoreceptor and the developing electrodes from the pores or slits by means of pressure, it has also been found that the relative speed between the photoreceptor and the liquid developer becomes locally abnormal and streaks are formed.